Influence of cork powder grainsize in thermal and mechanical properties of cork-NHL mortars

Cork is a unique material, characterized by small closed cell structures, high insulating properties, very low density, high fire resistance and a very good durability after simple thermal treatment. The main use of cork in the production of stopper and insulating panels obtained with cork grains and a polymeric resin. Usually cork grains used in panel production have a grainsize around 1-2 mm. In this work cork grains have been used as aggregates for natural hydraulic lime mortars by reducing grainsize distribution. Cork grainsize has been reduced by means of a knife mill and divided in three different distributions, i.e. 1, 0.5 and 0.25mm. Mortars have been prepared according to NHL to cork to natural sand volume ratio equal to 2:3:2. Three point bending and compression tests showed that reducing cork grainsize leads to a slight increase in mechanical performance. On the other hand thermal conductivity showed to be independent from cork grainsize. Scanning electron microscope investigation was also performed to better understand these results.